Aufbau principle of complex open-framework structures of metal phosphates with different dimensionalities

Open-framework metal phosphates occur as one-dimensional (1D] chains or lad ders, two-dimensional (2D) Layers, and complex three-dimensional (3D) struc tures. Zero-dimensional monomers have also been isolated recently. These ma terials are traditionally prepared by hydrothermal means, in the presence o f organic amines, but the reactions of amine phosphates with metal ions pro vide a facile route for the synthesis, and also throw some light on the mod e of formation of these fascinating architectures. Careful studies of the t ransformations of monophasic zinc phosphates of well-characterized structur es show that the 1D structures transform to 2D and 3D structures, while the 2D structures transform to 3D structures. The zero-dimensional monomers tr ansform to 1D, 2D, and 3D structures. There is reason to believe that the O D monomers, comprising four-membered rings, are the most basic structural u nits of the open-framework phosphates and that after an optimal precursor s tate, such as the ladder structure, is formed, further building may occur s pontaneously. Evidence for the occurrence of self-assembly in the formation of complex structures is provided by the presence of the structural featur es of the one-dimensional starting material in the final products. These ob servations constitute the beginning of our understanding of the building-up principle of such complex structures.